The present application relates generally to battery systems for any vehicle deriving at least a portion of its motive power from an electric power source (i.e., xEVs).
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Vehicles, such as cars, trucks, vans, are widely used to facilitate the movement of people and goods in modern society. Vehicles may utilize a number of different energy sources (e.g., a hydrocarbon fuel, a battery system, a capacitance system, a compressed air system) in order to produce motive power. In particular, the term “xEV” may be used to describe any vehicle that derives at least a portion of its motive power from an electric power source (e.g., a battery system). For example, electric vehicles (EVs), which may also be referred to as all-electric vehicles, typically include a battery system and use electric power for all of their motive power. As such, EVs may be principally dependent on a plug-in power source to charge a battery system, while other power generation/conservation systems (e.g., regenerative braking systems) may help extend the life of the battery and the range of the EV during operation.
Two specific sub-classes of xEV are the hybrid electric vehicle (HEV) and the plug-in hybrid electric vehicle (PHEV). Both the HEV and the PHEVs generally include an internal combustion engine in addition to a battery system. For the PHEV, as the name suggests, the battery system is capable of being charged from a plug-in power source. A series hybrid vehicle (e.g., a series PHEV or HEV) uses the internal combustion engine to turn a generator that, in turn, supplies current to an electric motor to move the vehicle. In contrast, a parallel hybrid (e.g., a parallel PHEV or HEV) can simultaneously provide motive power from an internal combustion engine and a battery powered electric drive system. That is, certain xEVs may use electrical energy stored in the battery system to boost (i.e., provide additional power to) the powertrain of the vehicle. Furthermore, xEVs (e.g., PHEVs and HEVs) may take advantage of opportunistic energy capture (e.g., via regenerative braking systems or similar energy conservation systems) in addition to using at least a portion of the power from the engine to charge the battery system.
In general, xEVs may provide a number of advantages as compared to traditional, gas-powered vehicles that solely rely on internal combustion engines for motive power. For example, xEVs may produce fewer undesirable emission products and may exhibit greater fuel efficiency as compared to vehicles using only internal combustion engines to propel the vehicle. Furthermore, for some xEVs, such as all-electric EVs that lack an internal combustion engine, the use of gasoline may be eliminated entirely.
As xEV technology continues to evolve, there is a need to provide improved power sources (e.g., battery systems) for such vehicles. That is, it is generally desirable to increase the distance that such vehicles may travel without the need to recharge the batteries. It is also desirable to improve the performance of such batteries and to reduce the cost associated with the battery systems. The battery systems of early electric vehicles employed nickel-metal-hydride (NiMH) cells. Over time, different additives and modifications have improved the performance, reliability, and utility of NiMH batteries. More recently, some manufacturers have moved toward lithium-ion batteries for use in xEVs. There may be several advantages associated with using lithium-ion batteries for vehicle applications. For example, lithium-ion batteries have a higher charge density and specific power than NiMH batteries. In other words, lithium-ion batteries may be smaller and lighter than NiMH batteries while storing an equivalent amount of charge. For xEVs, smaller, lighter battery systems may allow for weight and space savings in the design of the xEV and/or allow manufacturers to provide a greater amount of power for the vehicle without increasing the weight of the vehicle or the space taken up by the battery system.
Just as the chemistry of the battery systems has developed, so have the electronics (e.g., battery control units) that monitor and control these battery systems. For example, since lithium-ion batteries may be more susceptible to variations in battery temperature than comparable NiMH batteries, more complex electronic systems (e.g., temperature sensors, logic units, etc.) may be used to monitor and regulate the temperatures of the lithium-ion battery systems, even as the temperature of the battery system fluctuates during operation of the xEV. Furthermore, as both NiMH and lithium-ion battery cells age, they may generally store less charge and/or provide a lower output current than at their beginning of life (BOL).